In working machines, such as a clamping device, a compressing device, or a spot welding device, typically, a considerably large driving force is not necessary in the first half of a working process and a large driving force is necessary in the second half of the working process. Therefore, as disclosed in Patent Literatures (PTLs) 1 to 3, fluid pressure cylinders used in such working machines increase thrust in the second half of a working stroke (forward stroke) of a piston rod by additionally including booster mechanisms having various structures.
The fluid pressure cylinder with a booster mechanism disclosed in each of PTLs 1 to 3 includes a booster piston in addition to a main piston for driving the piston rod. When the piston rod reaches a booster start position before a forward stroke end, a pressure fluid is supplied to the booster piston to move the booster piston forward so that thrust of the booster piston acts on the piston rod. Thus, the piston rod is moved forward by large combined thrust that is the sum of the thrust of the main piston and the thrust of the booster piston. Therefore, in the fluid pressure cylinder with a booster mechanism, in addition to a port for causing the pressure fluid to act on the main piston, a port for causing the pressure fluid to act on the booster piston is necessary. Accordingly, the number of pipes becomes larger than that of an ordinary fluid pressure cylinder.
On the other hand, for a working machine including such a fluid pressure cylinder with a booster mechanism, it is required that the number of pipes be reduced as much as possible in order to increase safety by preventing damage to pipes around the fluid pressure cylinder due to contact with peripheral equipment and in order to simplify the operation of connecting pipes and the maintenance and management of pipes.